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// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package abi
import (
"cmd/compile/internal/types"
"cmd/internal/src"
"fmt"
"sync"
)
//......................................................................
//
// Public/exported bits of the ABI utilities.
//
// ABIParamResultInfo stores the results of processing a given
// function type to compute stack layout and register assignments. For
// each input and output parameter we capture whether the param was
// register-assigned (and to which register(s)) or the stack offset
// for the param if is not going to be passed in registers according
// to the rules in the Go internal ABI specification (1.17).
type ABIParamResultInfo struct {
inparams []ABIParamAssignment // Includes receiver for method calls. Does NOT include hidden closure pointer.
outparams []ABIParamAssignment
offsetToSpillArea int64
spillAreaSize int64
inRegistersUsed int
outRegistersUsed int
config *ABIConfig // to enable String() method
}
func (a *ABIParamResultInfo) Config() *ABIConfig {
return a.config
}
func (a *ABIParamResultInfo) InParams() []ABIParamAssignment {
return a.inparams
}
func (a *ABIParamResultInfo) OutParams() []ABIParamAssignment {
return a.outparams
}
func (a *ABIParamResultInfo) InRegistersUsed() int {
return a.inRegistersUsed
}
func (a *ABIParamResultInfo) OutRegistersUsed() int {
return a.outRegistersUsed
}
func (a *ABIParamResultInfo) InParam(i int) *ABIParamAssignment {
return &a.inparams[i]
}
func (a *ABIParamResultInfo) OutParam(i int) *ABIParamAssignment {
return &a.outparams[i]
}
func (a *ABIParamResultInfo) SpillAreaOffset() int64 {
return a.offsetToSpillArea
}
func (a *ABIParamResultInfo) SpillAreaSize() int64 {
return a.spillAreaSize
}
// RegIndex stores the index into the set of machine registers used by
// the ABI on a specific architecture for parameter passing. RegIndex
// values 0 through N-1 (where N is the number of integer registers
// used for param passing according to the ABI rules) describe integer
// registers; values N through M (where M is the number of floating
// point registers used). Thus if the ABI says there are 5 integer
// registers and 7 floating point registers, then RegIndex value of 4
// indicates the 5th integer register, and a RegIndex value of 11
// indicates the 7th floating point register.
type RegIndex uint8
// ABIParamAssignment holds information about how a specific param or
// result will be passed: in registers (in which case 'Registers' is
// populated) or on the stack (in which case 'Offset' is set to a
// non-negative stack offset. The values in 'Registers' are indices
// (as described above), not architected registers.
type ABIParamAssignment struct {
Type *types.Type
Name types.Object // should always be *ir.Name, used to match with a particular ssa.OpArg.
Registers []RegIndex
offset int32
}
// Offset returns the stack offset for addressing the parameter that "a" describes.
// This will panic if "a" describes a register-allocated parameter.
func (a *ABIParamAssignment) Offset() int32 {
if len(a.Registers) > 0 {
panic("Register allocated parameters have no offset")
}
return a.offset
}
// SpillOffset returns the offset *within the spill area* for the parameter that "a" describes.
// Registers will be spilled here; if a memory home is needed (for a pointer method e.g.)
// then that will be the address.
// This will panic if "a" describes a stack-allocated parameter.
func (a *ABIParamAssignment) SpillOffset() int32 {
if len(a.Registers) == 0 {
panic("Stack-allocated parameters have no spill offset")
}
return a.offset
}
// FrameOffset returns the location that a value would spill to, if any exists.
// For register-allocated inputs, that is their spill offset reserved for morestack
// (might as well use it, it is there); for stack-allocated inputs and outputs,
// that is their location on the stack. For register-allocated outputs, there is
// no defined spill area, so return -1.
func (a *ABIParamAssignment) FrameOffset(i *ABIParamResultInfo) int64 {
if len(a.Registers) == 0 || a.offset == -1 {
return int64(a.offset)
}
return int64(a.offset) + i.SpillAreaOffset()
}
// RegAmounts holds a specified number of integer/float registers.
type RegAmounts struct {
intRegs int
floatRegs int
}
// ABIConfig captures the number of registers made available
// by the ABI rules for parameter passing and result returning.
type ABIConfig struct {
// Do we need anything more than this?
offsetForLocals int64 // e.g., obj.(*Link).FixedFrameSize() -- extra linkage information on some architectures.
regAmounts RegAmounts
regsForTypeCache map[*types.Type]int
}
// NewABIConfig returns a new ABI configuration for an architecture with
// iRegsCount integer/pointer registers and fRegsCount floating point registers.
func NewABIConfig(iRegsCount, fRegsCount int, offsetForLocals int64) *ABIConfig {
return &ABIConfig{offsetForLocals: offsetForLocals, regAmounts: RegAmounts{iRegsCount, fRegsCount}, regsForTypeCache: make(map[*types.Type]int)}
}
// Copy returns a copy of an ABIConfig for use in a function's compilation so that access to the cache does not need to be protected with a mutex.
func (a *ABIConfig) Copy() *ABIConfig {
b := *a
b.regsForTypeCache = make(map[*types.Type]int)
return &b
}
// NumParamRegs returns the number of parameter registers used for a given type,
// without regard for the number available.
func (a *ABIConfig) NumParamRegs(t *types.Type) int {
var n int
if n, ok := a.regsForTypeCache[t]; ok {
return n
}
if t.IsScalar() || t.IsPtrShaped() {
if t.IsComplex() {
n = 2
} else {
n = (int(t.Size()) + types.RegSize - 1) / types.RegSize
}
} else {
typ := t.Kind()
switch typ {
case types.TARRAY:
n = a.NumParamRegs(t.Elem()) * int(t.NumElem())
case types.TSTRUCT:
for _, f := range t.FieldSlice() {
n += a.NumParamRegs(f.Type)
}
case types.TSLICE:
n = a.NumParamRegs(synthSlice)
case types.TSTRING:
n = a.NumParamRegs(synthString)
case types.TINTER:
n = a.NumParamRegs(synthIface)
}
}
a.regsForTypeCache[t] = n
return n
}
// preAllocateParams gets the slice sizes right for inputs and outputs.
func (a *ABIParamResultInfo) preAllocateParams(hasRcvr bool, nIns, nOuts int) {
if hasRcvr {
nIns++
}
a.inparams = make([]ABIParamAssignment, 0, nIns)
a.outparams = make([]ABIParamAssignment, 0, nOuts)
}
// ABIAnalyzeTypes takes an optional receiver type, arrays of ins and outs, and returns an ABIParamResultInfo,
// based on the given configuration. This is the same result computed by config.ABIAnalyze applied to the
// corresponding method/function type, except that all the embedded parameter names are nil.
// This is intended for use by ssagen/ssa.go:(*state).rtcall, for runtime functions that lack a parsed function type.
func (config *ABIConfig) ABIAnalyzeTypes(rcvr *types.Type, ins, outs []*types.Type) *ABIParamResultInfo {
setup()
s := assignState{
stackOffset: config.offsetForLocals,
rTotal: config.regAmounts,
}
result := &ABIParamResultInfo{config: config}
result.preAllocateParams(rcvr != nil, len(ins), len(outs))
// Receiver
if rcvr != nil {
result.inparams = append(result.inparams,
s.assignParamOrReturn(rcvr, nil, false))
}
// Inputs
for _, t := range ins {
result.inparams = append(result.inparams,
s.assignParamOrReturn(t, nil, false))
}
s.stackOffset = types.Rnd(s.stackOffset, int64(types.RegSize))
result.inRegistersUsed = s.rUsed.intRegs + s.rUsed.floatRegs
// Outputs
s.rUsed = RegAmounts{}
for _, t := range outs {
result.outparams = append(result.outparams, s.assignParamOrReturn(t, nil, true))
}
// The spill area is at a register-aligned offset and its size is rounded up to a register alignment.
// TODO in theory could align offset only to minimum required by spilled data types.
result.offsetToSpillArea = alignTo(s.stackOffset, types.RegSize)
result.spillAreaSize = alignTo(s.spillOffset, types.RegSize)
result.outRegistersUsed = s.rUsed.intRegs + s.rUsed.floatRegs
return result
}
// ABIAnalyze takes a function type 't' and an ABI rules description
// 'config' and analyzes the function to determine how its parameters
// and results will be passed (in registers or on the stack), returning
// an ABIParamResultInfo object that holds the results of the analysis.
func (config *ABIConfig) ABIAnalyze(t *types.Type) *ABIParamResultInfo {
setup()
s := assignState{
stackOffset: config.offsetForLocals,
rTotal: config.regAmounts,
}
result := &ABIParamResultInfo{config: config}
ft := t.FuncType()
result.preAllocateParams(t.NumRecvs() != 0, ft.Params.NumFields(), ft.Results.NumFields())
// Receiver
// TODO(register args) ? seems like "struct" and "fields" is not right anymore for describing function parameters
if t.NumRecvs() != 0 {
r := ft.Receiver.FieldSlice()[0]
result.inparams = append(result.inparams,
s.assignParamOrReturn(r.Type, r.Nname, false))
}
// Inputs
ifsl := ft.Params.FieldSlice()
for _, f := range ifsl {
result.inparams = append(result.inparams,
s.assignParamOrReturn(f.Type, f.Nname, false))
}
s.stackOffset = types.Rnd(s.stackOffset, int64(types.RegSize))
result.inRegistersUsed = s.rUsed.intRegs + s.rUsed.floatRegs
// Outputs
s.rUsed = RegAmounts{}
ofsl := ft.Results.FieldSlice()
for _, f := range ofsl {
result.outparams = append(result.outparams, s.assignParamOrReturn(f.Type, f.Nname, true))
}
// The spill area is at a register-aligned offset and its size is rounded up to a register alignment.
// TODO in theory could align offset only to minimum required by spilled data types.
result.offsetToSpillArea = alignTo(s.stackOffset, types.RegSize)
result.spillAreaSize = alignTo(s.spillOffset, types.RegSize)
result.outRegistersUsed = s.rUsed.intRegs + s.rUsed.floatRegs
// Fill in the frame offsets for receiver, inputs, results
k := 0
if t.NumRecvs() != 0 {
config.updateOffset(result, ft.Receiver.FieldSlice()[0], result.inparams[0], false)
k++
}
for i, f := range ft.Params.FieldSlice() {
config.updateOffset(result, f, result.inparams[k+i], false)
}
for i, f := range ft.Results.FieldSlice() {
config.updateOffset(result, f, result.outparams[i], true)
}
return result
}
func (config *ABIConfig) updateOffset(result *ABIParamResultInfo, f *types.Field, a ABIParamAssignment, isReturn bool) {
if !isReturn || len(a.Registers) == 0 {
// TODO in next CL, assign
if f.Offset+config.offsetForLocals != a.FrameOffset(result) {
if config.regAmounts.intRegs == 0 && config.regAmounts.floatRegs == 0 {
panic(fmt.Errorf("Expected node offset %d != abi offset %d", f.Offset, a.FrameOffset(result)))
}
}
}
}
//......................................................................
//
// Non-public portions.
// regString produces a human-readable version of a RegIndex.
func (c *RegAmounts) regString(r RegIndex) string {
if int(r) < c.intRegs {
return fmt.Sprintf("I%d", int(r))
} else if int(r) < c.intRegs+c.floatRegs {
return fmt.Sprintf("F%d", int(r)-c.intRegs)
}
return fmt.Sprintf("<?>%d", r)
}
// toString method renders an ABIParamAssignment in human-readable
// form, suitable for debugging or unit testing.
func (ri *ABIParamAssignment) toString(config *ABIConfig) string {
regs := "R{"
offname := "spilloffset" // offset is for spill for register(s)
if len(ri.Registers) == 0 {
offname = "offset" // offset is for memory arg
}
for _, r := range ri.Registers {
regs += " " + config.regAmounts.regString(r)
}
return fmt.Sprintf("%s } %s: %d typ: %v", regs, offname, ri.offset, ri.Type)
}
// toString method renders an ABIParamResultInfo in human-readable
// form, suitable for debugging or unit testing.
func (ri *ABIParamResultInfo) String() string {
res := ""
for k, p := range ri.inparams {
res += fmt.Sprintf("IN %d: %s\n", k, p.toString(ri.config))
}
for k, r := range ri.outparams {
res += fmt.Sprintf("OUT %d: %s\n", k, r.toString(ri.config))
}
res += fmt.Sprintf("offsetToSpillArea: %d spillAreaSize: %d",
ri.offsetToSpillArea, ri.spillAreaSize)
return res
}
// assignState holds intermediate state during the register assigning process
// for a given function signature.
type assignState struct {
rTotal RegAmounts // total reg amounts from ABI rules
rUsed RegAmounts // regs used by params completely assigned so far
pUsed RegAmounts // regs used by the current param (or pieces therein)
stackOffset int64 // current stack offset
spillOffset int64 // current spill offset
}
// align returns a rounded up to t's alignment
func align(a int64, t *types.Type) int64 {
return alignTo(a, int(t.Align))
}
// alignTo returns a rounded up to t, where t must be 0 or a power of 2.
func alignTo(a int64, t int) int64 {
if t == 0 {
return a
}
return types.Rnd(a, int64(t))
}
// stackSlot returns a stack offset for a param or result of the
// specified type.
func (state *assignState) stackSlot(t *types.Type) int64 {
rv := align(state.stackOffset, t)
state.stackOffset = rv + t.Width
return rv
}
// allocateRegs returns a set of register indices for a parameter or result
// that we've just determined to be register-assignable. The number of registers
// needed is assumed to be stored in state.pUsed.
func (state *assignState) allocateRegs() []RegIndex {
regs := []RegIndex{}
// integer
for r := state.rUsed.intRegs; r < state.rUsed.intRegs+state.pUsed.intRegs; r++ {
regs = append(regs, RegIndex(r))
}
state.rUsed.intRegs += state.pUsed.intRegs
// floating
for r := state.rUsed.floatRegs; r < state.rUsed.floatRegs+state.pUsed.floatRegs; r++ {
regs = append(regs, RegIndex(r+state.rTotal.intRegs))
}
state.rUsed.floatRegs += state.pUsed.floatRegs
return regs
}
// regAllocate creates a register ABIParamAssignment object for a param
// or result with the specified type, as a final step (this assumes
// that all of the safety/suitability analysis is complete).
func (state *assignState) regAllocate(t *types.Type, name types.Object, isReturn bool) ABIParamAssignment {
spillLoc := int64(-1)
if !isReturn {
// Spill for register-resident t must be aligned for storage of a t.
spillLoc = align(state.spillOffset, t)
state.spillOffset = spillLoc + t.Size()
}
return ABIParamAssignment{
Type: t,
Name: name,
Registers: state.allocateRegs(),
offset: int32(spillLoc),
}
}
// stackAllocate creates a stack memory ABIParamAssignment object for
// a param or result with the specified type, as a final step (this
// assumes that all of the safety/suitability analysis is complete).
func (state *assignState) stackAllocate(t *types.Type, name types.Object) ABIParamAssignment {
return ABIParamAssignment{
Type: t,
Name: name,
offset: int32(state.stackSlot(t)),
}
}
// intUsed returns the number of integer registers consumed
// at a given point within an assignment stage.
func (state *assignState) intUsed() int {
return state.rUsed.intRegs + state.pUsed.intRegs
}
// floatUsed returns the number of floating point registers consumed at
// a given point within an assignment stage.
func (state *assignState) floatUsed() int {
return state.rUsed.floatRegs + state.pUsed.floatRegs
}
// regassignIntegral examines a param/result of integral type 't' to
// determines whether it can be register-assigned. Returns TRUE if we
// can register allocate, FALSE otherwise (and updates state
// accordingly).
func (state *assignState) regassignIntegral(t *types.Type) bool {
regsNeeded := int(types.Rnd(t.Width, int64(types.PtrSize)) / int64(types.PtrSize))
if t.IsComplex() {
regsNeeded = 2
}
// Floating point and complex.
if t.IsFloat() || t.IsComplex() {
if regsNeeded+state.floatUsed() > state.rTotal.floatRegs {
// not enough regs
return false
}
state.pUsed.floatRegs += regsNeeded
return true
}
// Non-floating point
if regsNeeded+state.intUsed() > state.rTotal.intRegs {
// not enough regs
return false
}
state.pUsed.intRegs += regsNeeded
return true
}
// regassignArray processes an array type (or array component within some
// other enclosing type) to determine if it can be register assigned.
// Returns TRUE if we can register allocate, FALSE otherwise.
func (state *assignState) regassignArray(t *types.Type) bool {
nel := t.NumElem()
if nel == 0 {
return true
}
if nel > 1 {
// Not an array of length 1: stack assign
return false
}
// Visit element
return state.regassign(t.Elem())
}
// regassignStruct processes a struct type (or struct component within
// some other enclosing type) to determine if it can be register
// assigned. Returns TRUE if we can register allocate, FALSE otherwise.
func (state *assignState) regassignStruct(t *types.Type) bool {
for _, field := range t.FieldSlice() {
if !state.regassign(field.Type) {
return false
}
}
return true
}
// synthOnce ensures that we only create the synth* fake types once.
var synthOnce sync.Once
// synthSlice, synthString, and syncIface are synthesized struct types
// meant to capture the underlying implementations of string/slice/interface.
var synthSlice *types.Type
var synthString *types.Type
var synthIface *types.Type
// setup performs setup for the register assignment utilities, manufacturing
// a small set of synthesized types that we'll need along the way.
func setup() {
synthOnce.Do(func() {
fname := types.BuiltinPkg.Lookup
nxp := src.NoXPos
unsp := types.Types[types.TUNSAFEPTR]
ui := types.Types[types.TUINTPTR]
synthSlice = types.NewStruct(types.NoPkg, []*types.Field{
types.NewField(nxp, fname("ptr"), unsp),
types.NewField(nxp, fname("len"), ui),
types.NewField(nxp, fname("cap"), ui),
})
synthString = types.NewStruct(types.NoPkg, []*types.Field{
types.NewField(nxp, fname("data"), unsp),
types.NewField(nxp, fname("len"), ui),
})
synthIface = types.NewStruct(types.NoPkg, []*types.Field{
types.NewField(nxp, fname("f1"), unsp),
types.NewField(nxp, fname("f2"), unsp),
})
})
}
// regassign examines a given param type (or component within some
// composite) to determine if it can be register assigned. Returns
// TRUE if we can register allocate, FALSE otherwise.
func (state *assignState) regassign(pt *types.Type) bool {
typ := pt.Kind()
if pt.IsScalar() || pt.IsPtrShaped() {
return state.regassignIntegral(pt)
}
switch typ {
case types.TARRAY:
return state.regassignArray(pt)
case types.TSTRUCT:
return state.regassignStruct(pt)
case types.TSLICE:
return state.regassignStruct(synthSlice)
case types.TSTRING:
return state.regassignStruct(synthString)
case types.TINTER:
return state.regassignStruct(synthIface)
default:
panic("not expected")
}
}
// assignParamOrReturn processes a given receiver, param, or result
// of field f to determine whether it can be register assigned.
// The result of the analysis is recorded in the result
// ABIParamResultInfo held in 'state'.
func (state *assignState) assignParamOrReturn(pt *types.Type, n types.Object, isReturn bool) ABIParamAssignment {
state.pUsed = RegAmounts{}
if pt.Width == types.BADWIDTH {
panic("should never happen")
} else if pt.Width == 0 {
return state.stackAllocate(pt, n)
} else if state.regassign(pt) {
return state.regAllocate(pt, n, isReturn)
} else {
return state.stackAllocate(pt, n)
}
}